code: def _do_surface_dots_subset(
      intrad,
      rsurf,
      rmags,
      rref,
      refl,
      lsurf,
      rlens,
      this_nn,
      cosmags,
      ws,
      volume,
      lut,
      n_fact,
      ch_type,
      idx,
  ):
      """Parallelize.
  
      Parameters
      ----------
      refl : array | None
          If ch_type is 'eeg', the magnitude of position vector of the
          virtual reference (never used).
      lsurf : array
          Magnitude of position vector of the surface points.
      rlens : list of arrays of length n_coils
          Magnitude of position vector.
      this_nn : array, shape (n_vertices, 3)
          Surface normals.
      cosmags : list of array.
          Direction of the integration points in the coils.
      ws : list of array
          Integration weights of the coils.
      volume : bool
          If True, compute volume integral.
      lut : callable
          Look-up table for evaluating Legendre polynomials.
      n_fact : array
          Coefficients in the integration sum.
      ch_type : str
          'meg' or 'eeg'
      idx : array, shape (n_coils x 1)
          Index of coil.
  
      Returns
      -------
      products : array, shape (n_coils, n_coils)
          The integration products.
      """
      products = _fast_sphere_dot_r0(
          intrad,
          rsurf,
          rmags,
          lsurf,
          rlens,
          this_nn,
          cosmags,
          None,
          ws,
          volume,
          lut,
          n_fact,
          ch_type,
      ).T
      if rref is not None:
          raise NotImplementedError  # we don't ever use this, isn't tested
          # vres = _fast_sphere_dot_r0(
          #     intrad, rref, rmags, refl, rlens, this_nn, cosmags, None, ws,
          #     volume, lut, n_fact, ch_type)
          # products -= vres
      return products
  
file_path: mne-python/mne/forward/_lead_dots.py
imports: import os
  import os.path
  import numpy
  from numpy.polynomial import legendre
  from ..parallel import parallel_func
  from ..utils import _get_extra_data_path, fill_doc, logger, verbose
label_desc: Use image node_id 12 for calling a global function with example usage: _do_surface_dots_subset(intrad, rsurf, rmags, rref, refl, lsurf, rlens, this_nn, cosmags, ws, volume, lut, n_fact, ch_type, idx) and returns: products